Polydimethylsiloxane sheet, optical element incorporating the same, and manufacturing method thereof

ABSTRACT

A method of manufacturing a PDMS sheet that ensures good adhesion, handleability and stability to metal thin films or metal patterns of any desired shape. Given a low-molecular-weight siloxane of a cyclic structure represented by [—Si(CH 3 ) 2 O—] k  where k is an integer of 3 to 20 inclusive, the polydimethylsiloxane sheet has a structure where the content of the low-molecular-weight siloxane at the pattern-formation surface is more than that of the low-molecular-weight siloxane at the base surface, and a spacing between the adjacent metal patterns is variable by deformation of the polydimethylsiloxane sheet.

This is a divisional of application Ser. No. 13/405,940 filed Feb. 27,2012, and claims the benefit of Japanese Application No. 2011-046011filed Mar. 3, 2011. The entire disclosures of the prior applications arehereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to a polydimethylsiloxane sheet,and more particularly to a polydimethylsiloxane sheet for the formationof a metal thin film and a metal pattern shaped as desired, an opticalelement having a plurality of nano-order metal patterns formed on aflexible resin substrate, and a manufacturing method thereof.

So far, polydimethylsiloxane (hereinafter often abbreviated as PDMS)sheets have been advantageously used in a variety of application fieldsinclusive of electronic and electric devices or the like because ofexcelling in heat resistance, cold resistance and weather resistance andhaving stabilized electric characteristics.

Optical elements having a diffraction grating formed on a glasssubstrate or the like have also been widely used so far in the art, andmore recently, an optical element having a metal pattern formed on aflexible resin substrate has been proposed (the 56^(th) Spring Meeting,2009—The Japan Society of Applied Physics—by Oh Gyosei et. al. atUniversity of Tsukuba, 1p-H-9). This optical element changes in theinter-metal pattern nano-order locations upon receipt of external forceby the substrate, resulting in changes in the inter-metal patternnear-field interactions and, hence, optical responses. Another proposalhas been made of an optical element having zero reflectivity at aninterface with a substance without depending on the direction ofpolarization for 100% transmission of light (JP(A) 2006-350232). Thisoptical element has a structure in which a plurality of magneticresonators, each being a nano-structure wherein silver as ameta-material is C-shaped, are located on a glass substrate.

A problem with the conventional PDMS sheets, however, has been pooradhesion to metals. Another problem has been that when a PDMS sheet isplaced on a silicon-containing substrate such as a glass substrate, aquartz substrate or a silicon substrate to form a metal thin film or ametal pattern of any desired shape thereon, or stored on that substrateover an extended period of time, it may stick to the substrate, makinghandleability and stability worse.

Being flexible and transparent to light, the PDMS sheet could also beused as a flexible resin substrate forming a part of such an opticalelement as set forth in the aforesaid non-patent publication. However, aproblem with the direct formation of a metal pattern on the conventionalPDMS sheet, however, has been that the metal pattern peels off andde-bonds due to repetitive application of external force on the PDMSsheet, because there is a weak adhesion power of the metalnano-structure to the PDMS sheet.

DISCLOSURE OF THE INVENTION

A primary object of the invention is to provide a PDMS sheet that hasgood adhesion to a metal thin film or a metal pattern of any desiredshape and is improved in terms of handleability and stability, anoptical element that is protected against the peeling or de-bonding of ametal pattern and so has high reliability, and has good handleability,and manufacturing methods thereof.

In order to accomplish such an object, the invention disclosed hereinprovides an optical element comprising a polydimethylsiloxane sheethaving a pattern-formation surface defined by one surface and a basesurface defined by another surface, and a plurality of metal patternspositioned on said pattern-formation surface, wherein, given alow-molecular-weight siloxane of a cyclic structure represented by[—Si(CH₃)₂O—]_(k) where k is an integer of 3 to 20 inclusive, saidpolydimethylsiloxane sheet has a structure in which the content of saidlow-molecular-weight siloxane at said pattern-formation surface is morethan the content of said low-molecular-weight siloxane at said basesurface, and a spacing between adjacent said metal patterns is variableby deformation of said polydimethylsiloxane sheet.

The invention also provides an optical element comprising apolydimethylsiloxane sheet having a pattern-formation surface defined byone surface and a base surface defined by another surface, and aplurality of metal patterns positioned sais pattern-formation surface,wherein, given a low-molecular-weight siloxane of a cyclic structurerepresented by [—Si(CH₃)₂O—]_(k) where k is an integer of 3 to 20inclusive, said polydimethyl-siloxane sheet has a structure in which thecontent of said low-molecular-weight siloxane at said pattern-formationsurface is more than the content of said low-molecular-weight siloxaneat said base surface, and said metal patterns each comprise asubstantially ring-form pattern having a notch in at least a partthereof, and a space of said notch is variable by deformation of saidpolydimethylsiloxane sheet.

In one embodiment of the invention, the aforesaid polydimethylsiloxanesheet comprises on at least said pattern-formation surface ahigh-content polydimethyl-siloxane layer containing saidlow-molecular-weight siloxane in an amount of 2,000 ppm or more and onat least said base surface a low-content polydimethyl-siloxane layercontaining said low-molecular-weight siloxane in an amount of 1,000 ppmor less.

In another embodiment of the invention, said metal patterns contain anyof Au, Ag, and Al as a main component.

In a further embodiment of the invention, there is an underlay metallayer present between said polydimethyl-siloxane sheet and said metalpatterns, wherein said underlay metal layer has the same pattern as saidmetal patterns, or there is an underlay metal layer present between saidpolydimethylsiloxane sheet and said metal patterns, wherein saidunderlay metal layer is present all over said pattern-formation surfaceof said polydimethylsiloxane sheet.

In a further embodiment of the invention, said underlay metal layercontains any of Cr, Ti, Ni, W and an oxide and nitride thereof as a maincomponent.

In a further embodiment of the invention, said pattern-formation surfaceof said polydimethylsiloxane sheet has a surface average roughness Ra of0.1 μm or less.

In such an inventive optical element as described above, the metalpatterns are positioned on the high-content polydimethylsiloxane layer(pattern-formation surface) of the polydimethylsiloxane sheet; so theadhesion of the metal patterns to the polydimethyl-siloxane sheet isimproved, making sure high reliability. In addition, the low-contentpolydimethylsiloxane layer (base surface) of the polydimethylsiloxanesheet is of low reactivity to a silicone-containing substrate such as aglass, quartz, or silicon substrate; so even when thepolydimethylsiloxane sheet is placed and stored on such a substrate withits base surface abutting thereon, it is prevented from stickingthereto, making sure good handle-ability and stability.

Further, the invention provides a manufacturing method of the opticalelement of the invention, comprising a step of, given alow-molecular-weight siloxane of a cyclic structure represented by[—Si(CH₃)₂O—]_(k) where k is an integer of 3 to 20 inclusive, coating asupport substrate with a raw material for forming a low-contentpolydimethylsiloxane layer that contains said low-molecular-weightsiloxane in a smaller amount to form a coating film for the low-contentpolydimethylsiloxane layer, a step of feeding a raw material for forminga high-content polydimethylsiloxane layer that contains saidlow-molecular-weight siloxane in a larger amount on said coating filmfor the low-content polydimethylsiloxane layer and pressing a moldsubstrate against said raw material thereby forming a coating film forthe high-content polydimethylsiloxane layer between said mold substrateand said coating film for the low-content polydimethylsiloxane layer,after which said mold substrate is released from said coating film forthe high-content polydimethylsiloxane layer, a step of curing saidcoating film for the low-content polydimethyl-siloxane layer and saidcoating film for the high-content polydimethylsiloxane layer into apolydimethylsiloxane sheet comprising a structure of the low-contentpolydimethylsiloxane layer and the high-content polydimethylsiloxanelayer, a step of forming a plurality of metal patterns on apattern-formation surface defined by said high-contentpolydimethylsiloxane layer of said polydimethylsiloxane sheet in such away that a spacing between adjacent said metal patterns is 1,000 nm orless, and a step of releasing said polydimethylsiloxane sheet from saidsupport substrate.

Further, the invention provides a manufacturing method of the opticalelement of the invention, comprising a step of, given alow-molecular-weight siloxane of a cyclic structure represented by[—Si(CH₃)₂O—]_(k) where k is an integer of 3 to 20 inclusive, coating asupport substrate with a raw material for forming a low-contentpolydimethylsiloxane layer that contains said low-molecular-weightsiloxane in a smaller amount to form a coating film for the low-contentpolydimethylsiloxane layer, a step of feeding a raw material for forminga high-content polydimethylsiloxane layer that contains saidlow-molecular-weight siloxane in a larger amount on said coating filmfor the low-content polydimethylsiloxane layer and pressing a moldsubstrate onto said raw material thereby forming a coating film for thehigh-content polydimethylsiloxane layer between said mold substrate andsaid coating film for the low-content polydimethylsiloxane layer, afterwhich said mold substrate is released from the coating film for thehigh-content polydimethylsiloxane layer, a step of curing said coatingfilm for the low-content polydimethylsiloxane layer and said coatingfilm for the high-content poly-dimethylsiloxane layer into apolydimethylsiloxane sheet comprising a structure of the high-contentpolydimethyl-siloxane layer and the low-content polydimethylsiloxanelayer, a step of forming a plurality of metal patterns on apattern-formation surface defined by said high-contentpolydimethylsiloxane layer of said polydimethylsiloxane sheet, whereinsaid plurality of metal patterns each comprise a substantially ring-formpattern having a notch in at least a part thereof and a space of saidnotch is 1,000 nm or less, and a step of releasing saidpolydimethylsiloxane sheet from said support substrate.

In one embodiment of the invention, said low-contentpolydimethylsiloxane layer contains said low-molecular-weight siloxanein an amount of 1,000 ppm or less, and said high-contentpolydimethylsiloxane layer contains said low-molecular-weight siloxanein an amount of 2,000 ppm or more.

In another embodiment of the invention, said metal patterns are formedby forming a resist pattern on said pattern-formation surface of saidpolydimethylsiloxane sheet, then forming a metal layer on saidpattern-formation surface via said resist pattern, and finally peelingoff said resist pattern thereby lifting off the metal layer formed onthe resist pattern.

In yet another embodiment of the invention, said metal patterns areformed by forming a metal layer on said pattern-formation surface ofsaid polydimethyl-siloxane sheet, then forming a resist pattern on saidmetal layer, then etching said metal layer via said resist pattern, andfinally peeling off said resist pattern.

In a further embodiment of the invention, an underlay metal layer isformed all over said pattern-formation surface of saidpolydimethylsiloxane sheet, after which said metal patterns are formedon said underlay metal layer or, alternatively, an underlay metal layeris formed all over said pattern-formation surface of saidpolydimethylsiloxane sheet, after which said metal patterns are formedon said underlay metal layer, and a portion of said underlay metal layerwhere said metal patterns are not formed is removed by etching.

With such a manufacturing method of the optical element of the inventionas described above, the structure that is the polydimethylsiloxane sheetis formed, and the metal patterns are formed on the high-contentpolydimethylsiloxane layer (pattern-formation surface). This makes suretighter adhesion of the metal patterns to the polydimethylsiloxanesheet, and allows the low-content polydimethylsiloxane layer forming apart of the structure to be positioned on the support substrate side sothat the optical element can easily be released from the supportsubstrate.

Yet further, the invention provides a polydimethyl-siloxane sheetcomprising a structure that, given a low-molecular-weight siloxane of acyclic structure represented by [—Si(CH₃)₂O—]_(k) where k is an integerof 3 to 20 inclusive, has on at least one surface a high-contentpolydimethylsiloxane layer containing said low-molecular-weight siloxanein a larger amount and on at least another surface a low-contentpolydimethylsiloxane layer containing said low-molecular-weight siloxanein a smaller amount, wherein said high-content polydimethyl-siloxanelayer provides a work surface and said low-content polydimethylsiloxanelayer provides a base surface.

In one embodiment of the invention, said high-contentpolydimethylsiloxane layer contains said low-molecular-weight siloxanein an amount of 2,000 ppm or more, and said low-contentpolydimethylsiloxane layer contains said low-molecular-weight siloxanein an amount of 1,000 ppm or less.

In another embodiment of the invention, said structure has a thicknessin the range of 0.01 to 10 mm, and said low-content polydimethylsiloxanelayer has a thickness in the range of 0.005 to 5 mm.

In yet another embodiment of the invention, said work surface has asurface average roughness Ra of 0.1 μm or less.

Because the high-content polydimethylsiloxane layer that is the worksurface has so tight adhesion to metals, such an inventivepolydimethylsiloxane sheet as described above is well compatible withthe processing of metal thin films, metal patterns or the like so thatit can be applied to optical elements, flexible image display devices,flexible lighting devices and so on. In addition, the low-contentpolydimethylsiloxane layer that is the base surface is of low reactivityto silicon-containing substrates such as glass substrates, quartzsubstrates, and silicon substrates so that even when the inventivepolydimethylsiloxane sheet is placed and stored on such a substrate withthe base surface abutting thereon, it is prevented from sticking to thesubstrate enough to make sure good handleability and stability.

Still further, the invention provides a manufacturing method of apolydimethylsiloxane sheet comprising a step of, given alow-molecular-weight siloxane of a cyclic structure represented by[—Si(CH₃)₂O—]_(k) where k is an integer of 3 to 20 inclusive, coating asupport substrate with a raw material for forming a low-contentpoly-dimethylsiloxane layer that contains said low-molecular-weightsiloxane in a smaller amount to form a coating film for the low-contentpolydimethylsiloxane layer, a step of feeding a raw material for forminga high-content polydimethylsiloxane layer that contains thelow-molecular-weight siloxane in a larger amount on said coating filmfor the low-content polydimethylsiloxane layer and pressing a moldsubstrate onto said raw material thereby forming a coating film for ahigh-content polydimethylsiloxane layer, thereby forming a coating filmfor the high-content polydimethylsiloxane layer between said moldsubstrate and said coating film for the low-content polydimethylsiloxanelayer, after which said coating film for the high-contentpolydimethylsiloxane layer is released from said mold substrate, and astep of curing said coating film for the low-contentpolydimethylsiloxane layer and said coating film for the high-contentpolydimethylsiloxane layer into a polydimethyl-siloxane sheet comprisinga structure of the low-content polydimethylsiloxane layer and thehigh-content polydimethylsiloxane layer, after which said structure isreleased from said support substrate.

In one embodiment of the invention, said low-contentpolydimethylsiloxane layer contains said low-molecular-weight siloxanein an amount of 1,000 ppm or less, and said high-contentpolydimethylsiloxane layer contains said low-molecular-weight siloxanein an amount of 2,000 ppm or more.

In such a manufacturing method of the inventive polydimethylsiloxanesheet as described above, the low-content polydimethylsiloxane layer ispositioned on the support substrate side, notwithstanding the structurethat is the polydimethylsiloxane sheet comprises the high-contentpolydimethylsiloxane layer having good adhesion to metals, so that thestructure can easily be released from the support substrate. Inaddition, by proper determination of the shape of the mold substrate,any desired shape can be applied to the surface (work surface) of thehigh-content polydimethylsiloxane layer, making it possible tomanufacture polydimethylsiloxane sheets depending on the purpose.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary sectional view illustrative of one embodiment ofthe inventive polydimethylsiloxane sheet.

FIGS. 2A to 2F are a set of step diagrams illustrative of one embodimentof the manufacturing method of the inventive polydimethylsiloxane sheet.

FIG. 3 is a fragmentary plan view of one embodiment of the inventiveoptical element.

FIG. 4 is a longitudinally sectioned view of the optical element shownin FIG. 3, as taken on I-I line.

FIG. 5 is a longitudinally sectioned view, as in FIG. 4, of anotherembodiment of the inventive optical element.

FIG. 6 is a longitudinally sectioned view, as in FIG. 4, of yet anotherembodiment of the inventive optical element.

FIG. 7 is illustrative of how the inventive optical element shown inFIG. 3 operates.

FIG. 8 is a fragmentary plan view of a further embodiment of theinventive optical element.

FIG. 9 is a fragmentary plan view of a further embodiment of theinventive optical element.

FIG. 10 is a fragmentary plan view of a further embodiment of theinventive optical element.

FIG. 11 is a fragmentary plan view of a further embodiment of theinventive optical element.

FIG. 12 is a fragmentary plan view of a further embodiment of theinventive optical element.

FIGS. 13A to 13E are a set of step diagrams illustrative of oneembodiment of the manufacturing method of the inventive optical element.

FIGS. 14A to 14D are a set of step diagrams illustrative of oneembodiment of the manufacturing method of the inventive optical element.

DETAILED EXPLANATION OF THE INVENTION

Embodiments of the invention are now explained with reference to theaccompanying drawings.

[Polydimethylsiloxane Sheet]

FIG. 1 is a fragmentary sectional view illustrative of one embodiment ofthe inventive polydimethylsiloxane (PDMS) sheet. As shown in FIG. 1, theinventive PDMS sheet generally shown by reference numeral 1 is made upof a structure 2 comprising a high-content PDMS layer 3 containing thelow-molecular-weight siloxane in a larger amount and a low-content PDMSlayer 4 containing the low-molecular-weight siloxane in a smalleramount. More specifically, the PDMS sheet 1 is made up of the structure2 comprising the high-content PDMS layer 3 containing thelow-molecular-weight siloxane in an amount of 2,000 ppm or more,preferably in the range of 5,000 to 30,000 ppm and the low-content PDMSlayer 4 containing the low-molecular-weight siloxane in an amount of1,000 ppm or less, preferably in the range of 0 to 500 ppm. Here thehigh-content PDMS layer 3 side of the structure 2 provides a worksurface 3A for the formation of a metal thin film or a metal pattern ofany desired shape, and the low-content PDMS layer 4 side provides a basesurface 4A.

In the invention, the low-molecular-weight siloxane should have a cyclicstructure represented by [—Si(CH₃)₂O—]_(k) where k is an integer of 3 to20 inclusive due to the facts that it is of more reactivity to thesilicon-containing substrate than a high-molecular-weight siloxane, andthat its adhesion to metals and its reactivity to the silicon-containingsubstrate are controllable by its content. It is here to be noted thatthe content of the low-molecular-weight siloxane may be measured by gaschromatography after extraction by acetone. This holds true for thelow-molecular-weight siloxane and its content throughout the presentdisclosure.

As the content of the low-molecular-weight siloxane in the high-contentPDMS layer 3 forming a part of the PDMS sheet 1 is less than 2,000 ppm,it is not preferable in that the adhesion to metals becomesinsufficient, resulting in possible exfoliation and de-bonding of themetal thin film or the metal pattern of any desired shape formed on thehigh-content PDMS layer 3 (work surface 3A). As the content of thelow-molecular-weight siloxane in the low-content PDMS layer 4 is greaterthan 1,000 ppm, on the other hand, it is again not preferable in that inthe step of manufacturing the PDMS sheet 1 or in the processing step andstorage state of the PDMS sheet 1, the low-content PDMS layer 4 (basesurface 4A) may stick to the abutting substrate, for instance, asilicon-containing substrate such as a glass substrate, a quartzsubstrate, and a silicon substrate.

The inventive PDMS sheet 1 (structure 2) should have a thickness in therange of 0.01 to 10 mm, preferably 0.5 to 10 mm. As the thickness of thePDMS sheet 1 is less than 0.1 mm, it would render sheet manufacturingdifficult because the high viscosity of the raw material PDMS gives riseto sheet thickness variations and sheet ruptures upon peeling from thesupport substrate during manufacturing. As the thickness of the PDMSsheet 1 is greater than 10 mm, on the other hand, it is not preferablein that post-processing presumed for optical elements as an examplewould become difficult.

The low-content PDMS layer 4 forming a part of the PDMS sheet 1 couldhave a thickness in the range of 0.005 to 5 mm, preferably 0.05 to 1 mm.As the thickness of the low-content PDMS layer 4 is less than 0.005 mm,there would be defects in some of the low-content PDMS layer 4, whichmight render it impossible to apply the low-content PDMS layer 4 allover the base surface 4A of the PDMS sheet 1. As the thickness of thelow-content PDMS layer 4 is greater than 5 mm, on the other hand, it isnot preferable because the function of the low-content PDMS layer 4would not be enhanced any longer, and the manufacturing cost of the PDMSsheet 1 would increase as well.

The thickness of the high-content PDMS layer 3 forming a part of thePDMS sheet 1 is determined by setting the thickness of the PDMS sheet 1and the thickness of the low-content PDMS layer 4 in the aforesaidrange; there is no specific limitation on it. The PDMS sheet 1comprising the aforesaid structure 2 is provided for the purpose ofillustration alone; what is essentially needed here is that there is thehigh-content PDMS layer 3 present at the work surface 3A, and there isthe low-content PDMS layer 4 present at the base surface 4A. In otherwords, materials different from the high-content and low-content PDMSlayers 3 and 4 may exist between both layers 3 and 4 without departingfrom the purport disclosed herein. It is here to be noted that for theconvenience of explanation, the terminology “layer” is used to tell thehigh-content PDMS layer 3 from the low-content PDMS layer 4; however,the invention disclosed herein should not be interpreted as beinglimited to what is illustrated in the drawings. To put it another way,the polydimethylsiloxane sheet according to one embodiment of theinvention also embraces a structure having an ambiguous boundary betweenthe high-content PDMS layer 3 and the low-content PDMS layer 4. That is,although there is some difficulty in discerning the high-content andlow-content PDMS layers 3 and 4 as layers, respectively, yet theinvention disclosed herein also encompasses a structure in which thecontent of the low-molecular-weight siloxane in the work surface 3A is2,000 ppm or greater, and the content of the low-molecular-weightsiloxane in the base surface 4A is 1,000 ppm or less.

The shape of the surface (work surface 3A) of the high-content PDMSlayer 3 in the PDMS sheet 1 may optionally be determined depending onwhat purpose the PDMS sheet 1 is used for; for instance, when the PDMSsheet 1 is used for an optical element, that surface may be in a flatsurface form having a surface average roughness Ra of 0.1 μm or less. Itis here to be noted that the surface average roughness Ra may bemeasured under an atomic force microscope (AFM).

When the PDMS sheet 1 is used for an optical element, its lighttransmittance should be 80% or greater, preferably 90% or greater, morepreferably 95% or greater. The light transmittance here may be measuredby a spectrometer MCPD 2000 made by Otsuka Electronics Co., Ltd. ThePDMS sheet 1 should preferably have a coefficient of elasticity of 100kPa to 10 MPa in terms of tensile strength. The tensile strength herehas been measured on a universal testing machine Instron 5565 andexpressed in terms of the rupture strength of a dumbbell test piece.

Such inventive PDMS sheet 1 may be applied to optical elements, flexibleimage display devices, flexible lighting devices or the like, becausethe high-content PDMS layer 3 that is the work surface 3A shows goodadhesion to metals, making sure good processability for metal thinfilms, metal patterns or the like. In addition, the low-content PDMSlayer 4 that is the base surface 4A is of low reactivity tosilicon-containing substrates such as glass substrates, quartzsubstrates, and silicon substrates so that even when the PDMS sheet 1 isplaced and stored with the base surface abutting upon them, it isprevented from sticking to them, making sure good handleability andstability.

The aforesaid embodiment is given by way of exemplification but not byway of limitation.

[Manufacturing Method of the Polydimethylsiloxane Sheet]

FIGS. 2A to 2F are a set of step diagrams illustrative of one embodimentof the manufacturing method of the inventive polydimethylsiloxane sheetwherein the PDMS sheet 1 shown in FIG. 1 is used as an example.

First, the raw material for forming the low-content PDMS layer 4 iscoated on a support substrate 11 to form a coating film 14 for thelow-content PDMS layer (FIG. 2A). Given the low-molecular-weightsiloxane of a cyclic structure represented by [—Si(CH₃)₂O—]_(k) where kis an integer of 3 to 20 inclusive, the raw material used is a PDMScontaining the low-molecular-weight siloxane in a smaller amount, forinstance, a PDMS that has a low-molecular-weight siloxane content in therange of 1,000 ppm or less, preferably 0 to 500 ppm. For the supportsubstrate 11, there may be a rigid substrate used such as a glass,quartz, silicon or metal substrate, and the surface to be provided withthe coating film 14 should preferably be a flat surface having a surfaceaverage roughness Ra of, for instance, 0.1 μm or less in considerationof the thickness uniformity of the coating film 14 and the releasingfeature of the structure 2 from the support substrate 11 in a laterstep. The coating film 14 may be formed on the support substrate 11 asby spin coating, brush coating or other suitable coating, and thethickness of the coating film 14 may optionally be determined such thatthe thickness of the low-content PDMS layer 4 cured and formed in thelater step comes under the range of 0.005 to 5 mm, preferably 0.05 to 1mm. As the coating film 14 has a thickness such that the thickness ofthe low-content PDMS layer 4 cured and formed in the later step runsshort of 0.005 mm, it may possibly give rise to defects in some of thelow-content PDMS layer 4 formed, which would in turn render it difficultto release the structure 2 from the support substrate 11 in the laterstep, and cause the structure 2 to rupture or otherwise break. As thecoating film 14 has a thickness such that the thickness of thelow-content PDMS layer 4 exceeds 5 mm, on the other hand, it is notpreferable in that the function of the low-content PDMS layer 4 is notenhanced any longer, and the manufacturing cost of the PDMS sheet 1rises as well.

Next, a raw material 13′ for the formation of the high-content PDMSlayer 3 is fed onto the coating film 14 for the low-content PDMS layer(FIG. 2B), and a mold substrate 12 is then pressed against the rawmaterial 13′ thereby forming a coating film 13 for the high-content PDMSlayer between the mold substrate 12 and the coating film 14 for thelow-content PDMS layer (FIG. 2C), after which the coating film 13 isreleased from the mold substrate 12 (FIG. 2D). The raw material 13′ usedhere is a PDMS containing the low-molecular-weight siloxane in a largeramount, for instance, in the range of 2,000 ppm or greater, preferably5,000 to 30,000 ppm. By way of example but not by way of limitation,this raw material 13′ may be fed onto the coating film 14 for thelow-content PDMS layer, for instance, in a droplet form by means of adispenser. The thickness of the coating film 13 may optionally be setsuch that the thickness of the PDMS sheet 1 (structure 2) formed in alater step comes under the range of 0.01 to 10 mm, preferably 0.5 to 10mm. As the coating film 13 has a thickness such that the thickness ofthe structure 2 becomes less than 0.1 mm, it would render sheetmanufacturing difficult because the high viscosity of the raw material13′ would give rise to thickness variations and ruptures of thestructure 2 upon peeling from the support substrate 11. As the coatingfilm 13 has a thickness such that the thickness of the structure 2becomes greater than 10 mm, on the other hand, it is not preferable inthat the later step presumed for optical elements as an example wouldbecome difficult.

The mold substrate 12 is operable to turn the raw material 13′ into thecoating film 13, and to determine the shape of the surface (work surface3A) of the high-content PDMS layer 3 formed in the later step. For suchmold substrate 12, there may be a rigid substrate used such as a glass,quartz, silicon or metal substrate, and the shape of the surface of thatmold substrate to be pressed against the raw material 13′ (coating film13) may optionally be determined depending on the shape of the surface(works surface 3A) of the end high-content PDMS layer 3. For instance,when the PDMS sheet 1 is presumed for an optical element, that surfaceshould preferably be a flat surface having a surface average roughnessRa of up to 0.1 μm.

Finally, the coating film 13 for the high-content PDMS layer and thecoating film 14 for the low-content PDMS layer are cured into thestructure 2 made up of the high-content and low-content PDMS layers 3and 4 (FIG. 2E), after which the structure 2 is released from thesupport substrate 11 (FIG. 2F), whereby the inventive PDMS sheet 1 isobtained.

In order to form the coating film 13 for the high-content PDMS layer andthe coating film 14 for the low-content PDMS layer in the aforesaidembodiment of the manufacturing method of the PDMS sheet, reliance mayalso placed on two such methods as mentioned below. Referring to thefirst method, after the formation of the coating film 14 for thelow-content PDMS layer, the raw material 13′ for the formation of thehigh-content PDMS layer 3 is fed onto the coating film 14, and the moldsubstrate 12 is then pressed onto the material 13′ to form the coatingfilm 13 for the high-content PDMS layer. In that state, the coating film13 for the high-content PDMS layer and the coating film 14 for thelow-content PDMS layer are semi-cured. Finally, the coating film 13 forthe high-content PDMS layer is released from the mold substrate 12before the coating film 13 for the high-content PDMS layer and thecoating film 14 for the low-content PDMS layer are full-cured. Referringto the second method, the coating film 14 for the low-content PDMS layeris formed and semi-cured. Then, the raw material 13′ for the formationof the high-content PDMS layer 3 is fed onto the semi-cured coating film14 for the low-content PDMS layer, and the mold substrate 12 is pressedonto that material 13′ to form the coating film 13 for the high-contentPDMS layer. In that state, the coating film 13 is semi-cured (thecoating film 14 for the low-content PDMS layer may remain eitherfull-cured or semi-cured). Finally, the coating film 13 for thehigh-content PDMS layer is released from the mold substrate 12 beforethe coating film 13 for the high-content PDMS layer is full-cured. Inaccordance with these first and second methods, it is highly unlikelythat the coating film 13 for the high-content PDMS layer may remaintightly fixed to the mold substrate 12 because the mold substrate 12 ispeeled off while the coating film 13 for the high-content PDMS layer isin the semi-cured state. By forming the coating film 13 for thehigh-content PDMS layer in a state where the coating film 14 for thelow-content PDMS layer remains hardly cured or semi-cured, it ispossible to enhance the strength of the structure because the boundaryportions between both the coating layers are entangled up. Note herethat semi-curing may be achieved by letting the coating film alone atnormal temperature or heating it moderately.

Such inventive PDMS sheet manufacturing methods make sure the structure2 is easily releasable from the support plate 11, because thelow-content PDMS layer 4 is positioned on the support substrate 11 side,not with-standing the structure 2 that is the PDMS sheet 1 comprises thehigh-content PDMS layer 3 showing good adhesion to metals. A problemwith conventional PDMS sheet manufacturing is that handleability goesworse during manufacturing processes, because the PDMS sheet is releasedfrom the support substrate and then cured prior to the curing of thePDMS by heating. That problem can be overcome by the invention disclosedherein.

By optionally determining the shape of the mold substrate 12 accordingto the invention, it is possible to impart any desired shape to thesurface (work surface 3A) of the high-content PDMS layer, therebymanufacturing PDMS sheets depending on what purpose they are used for.

The aforesaid embodiments are given for the sake of exemplification, sothe invention is not limited to them whatsoever. For instance, when thePDMS sheet 1 is made up of a structure further comprising between thehigh-content and low-content PDMS layers 3 and 4 a resinous materialdifferent from both the layers, other resinous materials as desired maybe fed onto the coating film 14 for the low-content PDMS layer, ontowhich the raw material 13′ for the formation of the high-content PDMSlayer 3 is fed.

[Optical Element]

FIG. 3 is a fragmentary plan view illustrative of one embodiment of theoptical element according to the invention, and FIG. 4 is alongitudinally sectioned view of the optical element shown in FIG. 3 astaken on I-I line. As depicted in FIGS. 3 and 4, the inventive opticalelement generally indicated by reference numeral 21 comprises apolydimethylsiloxane (PDMS) sheet 31 having a pattern-formation surface33A defined by one surface and a base surface 34A defined by anothersurface, and a plurality of metal patterns 22 positioned on thepattern-formation surface 33A.

The PDMS sheet 31 transmits light and has flexibility; its lighttransmittance is at least 80%, preferably at least 90%, more preferablyat least 95%, and its coefficient of elasticity is in the range of 100kPa to 10 MPa in terms of tensile strength. Given a low-molecular-weightsiloxane having a cyclic structure represented by [—Si(CH₃)₂O—]_(k)where k is an integer of 3 to 20 inclusive, such PDMS sheet 31 is madeup of a structure 32 comprising a high-content PDMS layer 33 containingthe low-molecular-weight siloxane in a larger amount and a low-contentPDMS layer 34 containing the low-molecular-weight siloxane in a smalleramount. More specifically, the PDMS sheet 31 is made up of the structure32 comprising the high-content PDMS layer 33 containing thelow-molecular-weight siloxane in an amount of 2,000 ppm or more,preferably in the range of 5,000 to 30,000 ppm and the low-content PDMSlayer 34 containing the low-molecular-weight siloxane in an amount of1,000 ppm or less, preferably in the range of 0 to 500 ppm. Here thehigh-content PDMS layer 33 side of the structure 32 provides thepattern-formation surface 33A, and the low-content PDMS layer 34 sideprovides the base surface 34A. Being equivalent to the aforesaidinventive PDMS sheet 1 and the work surface 3A of the PDMS sheet 1, thePDMS sheet 31 and the pattern-formation surface 33A will not bediscussed in anymore detail. The PDMS sheet 31 comprising the aforesaidstructure 32 is provided for the purpose of illustration alone; what isessentially needed here is that there is the high-content PDMS layer 33present on the pattern-formation surface 33A, and there is thelow-content PDMS layer 34 present on the base surface 34A. In otherwords, materials different from the high-content and low-content PDMSlayers 33 and 34 may exist between both layers 3 and 4 without departingfrom the purport disclosed herein.

A plurality of metal patterns 22 positioned on the pattern-formationsurface 33A of the PDMS sheet 31 make up a metal nano-structure that hassuch a shape as to have rectangular projections at both ends of arectangle, as shown. Depending on the spacing D between the mostproximal metal patterns among such metal patterns 22, there is a changein the degree of near-field light interaction occurring across the metalnano-structure. Such spacing D may optionally be set depending on thewavelength of light applied to the optical element, usually at 1,000 nmor less. In order to have near-field light interaction to visible light,that spacing D should preferably be set in the range of 200 to 500 nm.Although the individual metal patterns 22 may optionally be sized, thatsize should preferably be 1,000 nm or less. Such metal patterns 22 maycontain as a main component, for instance, any of Au, Ag and Al, andhave a thickness in the range of 50 to 1,000 nm. The “main component”referred to herein is understood to mean the one accounting for at least50% by weight of the ingredients.

As shown in FIG. 5, the aforesaid inventive optical element may bemodified into an optical element 21′ having an underlay metal layer 23all over the pattern-formation surface 33A of the PDMS sheet 31, withthe metal patterns 22 positioned on that underlay metal layer 23.Alternatively, as shown in FIG. 6, it may be modified into an opticalelement 21″ having the metal patterns 22 on the pattern-formationsurface 33A via an underlay metal layer 23 subjected to the samepatterning as the metal patterns 22. Such underlay metal layer 23 isprovided for the purpose of making further improvements in the adhesionbetween the PDMS sheet 31 and the metal patterns 22. The underlay metallayer 23 may optionally be made up of a material without detrimental tothe operation and function of the optical element; for instance, it maincontain as a main component any of Cr, Ti, Ni, W and an oxide or nitridethereof. The underlay metal layer 23 may have a thickness typically inthe range of 1 to 5 nm.

Taking the optical element 21 shown in FIGS. 3 and 4 as an example, theoperation of the inventive optical element is now explained withreference to FIG. 7.

As the optical element 21 receives external bending force such that, forinstance, the side of the metal patterns 22 (the pattern-formationsurface 33A) projects out with stretching force acting in a directionindicated by a double-action arrow a in FIGS. 3 and 7, it causes thespacing between the adjacent metal patterns 22 to widen from D to D′.Such a change in the spacing between the adjacent metal patterns 22 endsup with a change in the near-field light interaction occurring betweenthe adjacent metal patterns 22. In turn, this causes light verticallyincident on the optical element 21 (in the direction indicated by adouble-action arrow b in FIG. 4) to change in its polarization state. Bymaking use of such a function of the optical element 21 and a polarizingfilter, that optical element can be used as, for example, a photonicswitch operable to put light on and off. If the spacing D between theadjacent metal patterns 22 is designed to come within the visible lightrange (400 to 700 nm), it is then possible to change the spacing Dbetween the metal patterns 22 by the application of predeterminedexternal force, thereby changing the polarization of incident lightincident in the visible light range. Thus, the inventive optical elementcan make the range of use wider than could be achieved with conventionalelements using a glass, quartz or other substrate.

It is here to be noted that the external force applied to the opticalelement 21 to change the spacing between the adjacent metal patterns 22is not limited to bending force; for instance, pulling force may begiven to the PDMS sheet 31 to stretch it in the direction indicated bythe double-action arrow a.

FIG. 8 is a fragmental plan view illustrative of another embodiment ofthe inventive optical element. As shown in FIG. 8, the inventive opticalelement generally indicated by reference numeral 41 is comprised of aPDMS sheet 51 having a pattern-formation surface 53A defined by onesurface and a base surface defined by another surface, and a pluralityof metal patterns 42 positioned on a high-content PDMS layer 53(pattern-formation surface 53A) of the PDMS sheet 51.

Being similar to the PDMS sheet 31 that forms the aforesaid opticalelement 21, the PDMS sheet 51 that forms the optical element 41 will notbe discussed in anymore detail.

A plurality of metal patterns 42 positioned on the pattern-formationsurface 53A of the PDMS sheet 51 make up a metal nano-structure whereinrectangular patterns are arrayed with longer sides lying proximate toone another, as shown. Depending on the spacing D between the mostproximate metal patterns among such metal patterns 42, there is a changein the degree of near-field light interaction occurring across the metalnano-structure. Such spacing D may optionally be set depending on thewavelength of light applied to the optical element, usually at 1,000 nmor less. In order to have near-field light interaction to visible light,that spacing D should preferably be set in the range of 200 to 500 nm.Although the individual metal patterns 42 may optionally be sized, thatsize should preferably be 1,000 nm or less. Such metal patterns 42 mayagain be formed of a material similar to that of the aforesaid metalpatterns 22.

The optical element 41, too, may have an underlay metal layer betweenthe pattern-formation surface 53A of the PDMS sheet 51 and the metalpatterns 42, as is the case with the aforesaid optical elements 21′ and22″.

As external force is applied to such optical element 41, it brings abouta change in the spacing D between the adjacent metal patterns 42 as isthe case with the aforesaid optical element 21, causing a change in thenear-field light interaction occurring between the adjacent metalpatterns 42.

Other embodiments of the inventive optical element are now explainedwith reference to FIGS. 9 to 12 showing an optical element functioningas a meta-material.

FIG. 9 is a fragmentary plan view illustrative of one embodiment of theinventive optical element functioning as a meta-material. As shown inFIG. 9, the inventive optical element generally indicated by referencenumeral 61 comprises a PDMS sheet 71 having a pattern-formation surface73A defined by one surface and a base surface defined by anothersurface, and a plurality of metal patterns 62 positioned on ahigh-content PDMS layer 73 (pattern-formation surface 73A) of the PDMSsheet 71.

Being similar to the PDMS sheet 31 that forms a part of the aforesaidoptical element 21, the PDMS sheet 71 that forms a part of the opticalelement 61 will not be discussed in anymore detail.

A plurality of metal patterns 62 positioned on the pattern-formationsurface 73A of the PDMS sheet 71 make up a metal nano-structure in whichsubstantially ring-form patterns, each one having one notch 62 a, arearrayed as shown. Depending on the notch space D of the notch 62 a ineach metal pattern 62, there is a change in the degree of near-fieldlight interaction occurring across the metal nano-structure. Suchspacing D may optionally be set depending on the wavelength of lightapplied to the optical element, usually at 1,000 nm or less. In order tohave near-field light interaction to visible light, that spacing Dshould preferably be set in the range of 200 to 500 nm. Although thedimension L of each metal pattern 62 and the array pitch P of the metalpatterns 62 may optionally be determined, yet L and P should preferablybe 1,000 nm or less. The “substantially ring-form” used herein isunderstood to refer to a ring that generally takes on an annular formalbeit having at least one notch, and the “annular form” is understoodto refer to a variety of forms inclusive of an annular ring, a squarering, and a polygonal ring; so an array of such substantially ring-formpatterns may be an array of square rings typically shown in FIG. 10,each one having one notch 62 a. Such metal patterns 62 may be formed ofthe same material as the aforesaid metal pattern 22 is formed of.

The optical element 61, too, may have an underlay metal layer betweenthe pattern-formation surface 73A of the PDMS sheet 71 and the metalpatterns 62, as is the case with the aforesaid optical elements 21′ and22″.

As external force is applied to such optical element 61, it brings abouta change in the notch space D of the notch 62 a in each substantiallyring-form metal pattern 62 as is the case with the aforesaid opticalelement 21, causing a change in the near-field light interactionoccurring across the metal nano-structure.

FIG. 11 is a fragmentary plan view illustrative of another embodiment ofthe inventive optical element functioning as a meta-material. As shownin FIG. 11, the inventive optical element generally indicated byreference numeral 81 comprises a PDMS sheet 91 having apattern-formation surface 93A defined by one surface and a base surfacedefined by another surface, and a plurality of metal patterns 82positioned on a high-content PDMS layer 93 (pattern-formation surface93A) of the PDMS sheet 91.

Being similar to the PDMS sheet 31 that forms a part of the aforesaidoptical element 21, the PDMS sheet 91 that forms a part of the opticalelement 81 will not be discussed in anymore detail.

A plurality of metal patterns 82 positioned on the pattern-formationsurface 93A of the PDMS sheet 91 make up a metal nano-structure in whichsubstantially ring-form patterns, each one having two notches 82 a and82 a, are arrayed as shown. Depending on the notch space D of thenotches 82 a and 82 a in each metal pattern 82, there is a change in thedegree of near-field light interaction occurring across the metalnano-structure. Such notch space D may optionally be set depending onthe wavelength of light applied to the optical element, usually at 1,000nm or less. In order to have near-field light interaction to visiblelight, that space D should preferably be set in the range of 200 to 500nm. Although the dimension L of each metal pattern 82 and the arraypitch P of the metal patterns 82 may optionally be determined, yet L andP should preferably be 1,000 nm or less. The metal patterns 82 may alsobe formed by an array of square rings, each one having two notches 82 aand 82 a as typically shown in FIG. 12. Such metal patterns 82 may beformed of the same material as the aforesaid metal pattern 22 is formedof.

The optical element 81, too, may have an underlay metal layer betweenthe pattern-formation surface 93A of the PDMS sheet 91 and the metalpatterns 82, as is the case with the aforesaid optical elements 21′ and22″.

As external force is applied to such optical element 81, it brings abouta change in the notch space D of the notches 82 a and 82 a in eachsubstantially ring-form metal pattern 82 as is the case with theaforesaid optical element 21, causing a change in the near-field lightinteraction occurring across the metal nano-structure.

Such an inventive optical element has ever higher reliability, becausethe metal patterns 22, 42, 62, 82 are positioned on the high-contentPDMS layer 33, 53, 73, 93 (pattern-formation surface) so that there isgood adhesion achievable between the metal patterns and the PDMS sheet.The low-content PDMS layer 34 (base surface 34A) of the PDMS sheet is oflow reactivity to a silicon-containing substrate such as a glass,quartz, and silicon substrate so that even when it is placed and storedwith its base surface abutting on that substrate, it is prevented fromsticking to the substrate, making sure good handleability and stability.

The aforesaid embodiments are given by way of exemplification; so theinvention is not limited thereto whatsoever. For instance, the aforesaidoptical elements 61 may be stacked one upon another into the inventiveoptical element. In that case, the positions of the notches 62 a in thesubstantially ring-form metal patterns 62 on the optical elementsforming the layers may be aligned in the stacking direction, or thepositions of the notches 62 a may be displaced for each one layer ordepending on multiple layers. Alternatively, the positions of thenotches 62 a may be disposed at random for each one layer. How manyoptical elements, each one having such structure, are stacked togethermay optionally be determined depending on the optical characteristicsdemanded, what purpose the optical elements are used for, or the like.The optical element of such stacked structure may also be set up usingthe aforesaid optical element 81.

[Manufacturing Method of the Optical Element]

FIGS. 13A to 13E, and FIGS. 14A to 14D are a set of step diagramsillustrative of one embodiment of the inventive optical element, whereinthe optical element 21 shown in FIGS. 3 and 4 is used as an example.

In the manufacturing method of the inventive optical element, first ofall, a raw material for the formation of a low-content PDMS layer 34 iscoated on a support substrate 37 to form a coating film 34′ for thelow-content PDMS layer (FIG. 13A). Given the low-molecular-weightsiloxane of a cyclic structure represented by [—Si(CH₃)₂O—]_(k) where kis an integer of 3 to 20 inclusive, the raw material used is a PDMScontaining the low-molecular-weight siloxane in a smaller amount, forinstance, a PDMS that has a low-molecular-weight siloxane content in therange of 1,000 ppm or less, preferably 0 to 500 ppm. For the supportsubstrate 37, there may be a rigid substrate used such as a glass,quartz, silicon or metal substrate, and the surface to be provided withthe coating film 34′ should preferably be a flat surface having asurface average roughness Ra of, for instance, 0.1 μm or less inconsideration of the thickness uniformity of the coating film 34′ andthe releasing feature of the structure 32 from the support substrate ina later step.

The coating film 34′ may be formed on the support substrate 37 as byspin coating, brush coating or other suitable coating, and the thicknessof the coating film 34′ may optionally be determined such that thethickness of the low-content PDMS layer 34 cured and formed in the laterstep comes under the range of 0.005 to 5 mm, preferably 0.05 to 1 mm. Asthe coating film 34′ has a thickness such that the thickness of thelow-content PDMS layer 34 cured and formed in the later step runs shortof 0.005 mm, it may possibly give rise to defects in some of thelow-content PDMS layer 34 formed, which would in turn render itdifficult to release the structure 32 from the support substrate 37 inthe later step, and cause the structure 32 to rupture or otherwisebreak. As the coating film 34′ has a thickness such that the thicknessof the low-content PDMS layer 34 exceeds 5 mm, on the other hand, it isnot preferable in that the function of the low-content PDMS layer 34would not be enhanced any longer, and the manufacturing cost of the PDMSsheet 21 rises as well.

Next, a raw material 33″ for the formation of the high-content PDMSlayer 33 is fed onto the coating film 34′ for the low-content PDMS layer(FIG. 13B), and a mold substrate 38 is then pressed against that rawmaterial 33″ thereby forming a coating film 33′ for the high-contentPDMS layer between the mold substrate 38 and the coating film 34′ forthe low-content PDMS layer (FIG. 13C), after which the coating film 33′is released from the mold substrate 38 (FIG. 13D). The raw material 33″used here is a PDMS containing the low-molecular-weight siloxane in alarger amount, for instance, in the range of 2,000 ppm or greater,preferably 5,000 to 30,000 ppm. By way of example but not by way oflimitation, this raw material 33″ may be fed onto the coating film 14for the low-content PDMS layer, for instance, in a droplet form by meansof a dispenser. The thickness of the coating film 33′ may optionally beset such that the thickness of the PDMS sheet 31 (structure 32) formedin a later step comes under the range of 0.01 to 10 mm, preferably 0.5to 10 mm. As the coating film 33′ has a thickness such that thethickness of the structure 32 becomes less than 0.1 mm, it would rendersheet manufacturing difficult because the high viscosity of the rawmaterial 33″ would give rise to thickness variations and ruptures of thestructure 32 upon peeling from the support substrate 37. As the coatingfilm 33′ has a thickness such that the thickness of the structure 32becomes greater than 10 mm, on the other hand, it is not preferable inthat the formation of the metal patterns 22 in the later step wouldbecome difficult.

The mold substrate 38 is operable to turn the raw material 33″ into thecoating film 33′, and to determine the shape of the surface (worksurface 33A) of the high-content PDMS layer 33 formed in the later step.For such mold substrate 38, there may be a rigid substrate used such asa glass, quartz, silicon or metal substrate, and the shape of thesurface of that mold substrate to be pressed against the raw material33″ (coating film 33′) should preferably be a flat surface having asurface average roughness Ra of 0.1 μm or less.

Finally, the coating film 33′ for the high-content PDMS layer and thecoating film 34′ for the low-content PDMS layer are cured to form on thesupport substrate 37 the structure 32 made up of the high-content andlow-content PDMS layers 33 and 34 (FIG. 13E).

In the aforesaid manufacturing embodiment, the coating film 33′ for thehigh-content PDMS layer may be either hardly cured or semi-cured upon areleasing of the coating film 33′ from the mold substrate 38 (FIG. 13D).At this time, the coating film 34′ for the low-content PDMS layer may beeither full-cured or semi-cured. For instance, the coating film 34′ forthe low-content PDMS layer may have been semi-cured for the formation ofthe coating film 33′ for the high-content PDMS layer, in which case theboundary portions between the coating film 34′ for the low-content PDMSlayer and the coating film 33′ for the high-content PDMS layer areentangled up thereby enhancing the strength of the structure 32.

Then, a resist pattern 39 is formed on the surface (pattern-formationsurface 33A) of the high-content PDMS layer 33 in the structure 32 (FIG.14A), and a metal layer 22′ is formed in such a way as to cover thatresist pattern 39 (FIG. 14B). For instance, the resist pattern 39 may beformed by photolithography using a photo-sensible resist, and the metallayer 22′ may be formed by means of vacuum film-formation processes suchas sputtering or vacuum evaporation using a material containing Au, Ag,Al or the like as a main component, with a thickness in the range of 50to 1,000 nm.

Finally, the resist pattern 39 is removed, and the metal layer 22′ onthe resist pattern 39 is lifted off to form metal patterns 22 (FIG.14C). Thereafter, the structure 32 is released from the supportsubstrate 37 (FIG. 14D), whereby the inventive optical element 21 isobtainable.

In the aforesaid manufacturing method, the lift-off process by removalof the resist pattern 39 is used for the formation of the metal patterns22; however, the invention is not limited thereto at all. For instance,the vacuum film-formation process such as sputtering or vacuumevaporation using a material containing Au, Ag, Al or the like as a maincomponent may be used to form the metal layer on the surface(pattern-formation surface 33A) of the high-content PDMS layer 33 in thestructure 32, after which that metal layer is pattern etched to form themetal patterns 22.

When there is an optical element manufactured that has the metalpatterns 22 on the underlay metal layer 23 formed all over thepattern-formation surface 33A as is the case with the aforesaid opticalelement 21′, the structure 32 is first formed on the support substrate37 (FIG. 13E). Then, the underlay metal layer 23 is formed all over thepattern-formation surface 33A by means of the vacuum film-formationprocess such as sputtering or vacuum evaporation using a materialcontaining as a main component, for instance, any of Cr, Ti, Ni, W andan oxide or nitride thereof. Finally, the metal patterns 22 are formedas described above.

When there is an optical element manufactured that has the underlaymetal layer 23 in the same patterns as the metal patterns 22 as is thecase with the aforesaid optical element 21″, the structure 32 is firstformed on the support substrate 37 (FIG. 13E). Then, the underlay metallayer 23 is formed all over the pattern-formation surface 33A by meansof the vacuum film-formation process such as sputtering or vacuumevaporation using a material containing as a component, for instance,any of Cr, Ti, Ni, W and an oxide or nitride thereof. Then, the metallayer is formed on the underlay metal layer 23 by means of the vacuumfilm-formation process such as sputtering or vacuum evaporation using amaterial containing Au, Ag, Al or the like as a main component. Finally,pattern etching is applied to the metal layer and the underlay metallayer 23 to form the metal patterns 22 (the underlay metal layer 23 inthe same patterns as them).

In the manufacturing method of the inventive optical element, thestructure 32 that is the PDMS sheet 31 is formed, and the metal patterns22 are formed on the high-content PDMS layer 33 (pattern-formationsurface 33A) making up a part of the structure 32 so that the adhesionof the metal patterns 22 to the PDMS sheet 31 is much more enhanced. Thelow-content PDMS layer 34 making up a part of the structure 32 is sopositioned on the support substrate 37 side that the optical element 21is easily releasable from the support substrate 37.

The aforesaid embodiments are given by way of exemplification; so theinvention is not limited thereto whatsoever. For instance, when the PDMSsheet 31 is comprised of a structure in which a resinous materialdifferent from the high-content and low-content PDMS layers 33 and 34 isprovided between both the layers, other resinous material may be fedonto the coating film 34′ for the low-content PDMS layer to form acoating film, onto which the raw material 33″ for the formation of thehigh-content PDMS layer 33 is fed.

By way of example but not by way of limitation, the present inventionwill now be explained in further details with reference to some specificexamples.

Example 1

There was a silicon substrate of 0.625 mm in thickness and 150 mm indiameter provided as the support substrate. This support substrate wasfound to have a surface average roughness Ra of 0.001 μm as measured onAFM (L-Trace II made by Seiko Instruments Inc.).

After a polymerization initiator was mixed with a raw material A for theformation of the low-content PDMS layer, the mixture was spin coated onthe aforesaid support substrate to form a coating film A. Given thelow-molecular-weight siloxane of a cyclic structure represented by[—Si(CH₃)₂O—]_(k) where k is an integer of 3 to 20 inclusive, that rawmaterial A was a PDMS having a low-molecular-weight siloxane content of1,000 ppm. The thickness of the coating film A was set such that thelow-content PDMS layer formed by curing had a thickness of 0.1 mm.

Then, after a polymerization initiator was mixed with a raw material Bfor the formation of the high-content PDMS layer, the mixture (20 grams)was added dropwise to the coating film A for the low-content PDMS layerby means of a dispenser. This raw material B was a PDMS having alow-molecular-weight siloxane content of 2,000 ppm.

Then, the mold substrate (with a molding surface having a surfaceaverage roughness Ra of 0.001 μm) was pressed against the fed rawmaterial B to form a coating film B for the high-content PDMS layerbetween the mold substrate and the coating film A for the low-contentPDMS layer, in which state the coating film B was let alone at normaltemperature for semi-curing, followed by releasing the coating film Bfrom the mold substrate. Finally, the coating films A and B in thesemi-cured state was full-cured by heating into a structure (of 1.2 mmin thickness) made up of the high-content and low-content PDMS layers,and this structure was released from the support substrate to form aPDMS sheet.

Example 2

Example 1 was repeated with the exception that a PDMS having alow-molecular-weight siloxane content of 7,000 ppm was used as the rawmaterial B for the formation of the high-content PDMS layer, therebypreparing a PDMS sheet.

Example 3

Example 1 was repeated with the exception that a PDMS having alow-molecular-weight siloxane content of 200 ppm was used as the rawmaterial A for the formation of the low-content PDMS layer, therebypreparing a PDMS sheet.

Comparative Example 1

Example 1 was repeated with the exception that a PDMS having alow-molecular-weight siloxane content of 200 ppm was used as the rawmaterial A for the formation of the low-content PDMS layer and a PDMShaving a low-molecular-weight siloxane of 1,000 ppm was used as the rawmaterial B for the formation of the high-content PDMS layer, therebypreparing a PDMS sheet.

Comparative Example 2

Example 1 was repeated with the exception that a PDMS having alow-molecular-weight siloxane content of 1,500 ppm was used as the rawmaterial A for the formation of the low-content PDMS layer, therebypreparing a PDMS sheet.

Comparative Example 3

Example 1 was repeated with the exception that a PDMS having alow-molecular-weight siloxane content of 1,300 ppm was used as the rawmaterial A for the formation of the low-content PDMS layer and a PDMShaving a low-molecular-weight siloxane content of 1,700 ppm was used asthe raw material B for the formation of the high-content PDMS layer,thereby preparing a PDMS sheet.

[Estimation]

(Releasability)

How the structure was released from the support substrate in theaforesaid PDMS sheet preparation was observed to make estimation ofreleasability on the following criteria. The results are set out inTable 1 given later.

(Estimation Criteria)

◯: None of the structure remained sticking to the support substrate.

x: Some of the structure remained sticking to the support substrate.

(Adhesion to Metals, Especially Cr)

A Cr thin film (of 50 nm in thickness) was formed by sputtering on theside (work surface) of the high-content PDMS layer of the PDMS sheetprepared as described above, and the adhesion of that Cr thin film tothe PDMS sheet was estimated by the cross-cutting method was estimated.The results are set out in Table 1 given later. More specifically, theCr thin film was divided by a cutter knife into 100 square areas havingone side of 1 cm. After an adhesive-backed tape (Cellotape made byNichiban Co., Ltd.) was applied to all of 100 square areas, it waspulled right above to observe whether or not there was a peeling of theCr thin film and make estimation on the following estimation criteria.

(Estimation Criteria)

-   ◯: No peeling of the square areas off the Cr thin film or good    adhesion.-   x: Peeling from the square areas off the Cr thin film or poor    adhesion.    (Adhesion to Metals, Especially Au)

An Au thin film (of 50 nm in thickness) was formed by sputtering on theside (work surface) of the high-content PDMS layer of the PDMS sheetprepared as described above. The adhesion of that Au thin film to thePDMS sheet was measured as described above, and estimated on the samecriteria as described above. The results are set out in Table 1 givenlater.

(Stability)

The PDMS sheet prepared as described above was placed and maintained ona silicon substrate for 120 days while its low-content PDMS layer side(base surface) remained abutting onto it, after which whether or not thePDMS sheet remained sticking to the silicon substrate was observed. Theresults are set out in Table 1 given just below.

TABLE 1 Low-molecular-weight Adhesion to siloxane content (ppm) metalsPDMS sheet Raw material A Raw material B Releasability To Cr To AuStability Example 1 1,000 2,000 ∘ ∘ ∘ No sticking Example 2 1,000 7,000∘ ∘ ∘ No sticking Example 3 200 2,000 ∘ ∘ ∘ No sticking Comparative 2001,000 ∘ x x No sticking Example 1 Comparative 1,500 2,000 x ∘ ∘ SomeExample 2 sticking Comparative 1,300 1,700 x x x Some Example 3 sticking

What is claimed is:
 1. A method of manufacturing an optical element,comprising: a step of, given a low-molecular-weight siloxane of a cyclicstructure represented by [—Si(CH₃)₂O—]_(k) where k is an integer of 3 to20 inclusive, coating a support substrate with a raw material forforming a low-content polydimethylsiloxane layer that contains saidlow-molecular-weight siloxane in a smaller amount to form a coating filmfor the low-content polydimethylsiloxane layer, a step of feeding a rawmaterial for forming a high-content polydimethylsiloxane layer thatcontains said low-molecular-weight siloxane in a larger amount on saidcoating film for forming the low-content polydimethyl-siloxane layer andpressing a mold substrate against said raw material thereby forming acoating film for the high-content polydimethylsiloxane layer betweensaid mold substrate and said coating film for the low-contentpolydimethylsiloxane layer, after which said mold substrate is releasedfrom said coating film for the high-content polydimethylsiloxane layer,a step of curing said coating film for the low-contentpolydimethylsiloxane layer and said coating film for the high-contentpolydimethylsiloxane layer into a polydimethylsiloxane sheet comprisinga structure of the low-content polydimethylsiloxane layer and thehigh-content polydimethylsiloxane layer, a step of forming a pluralityof metal patterns on a pattern-formation surface defined by saidhigh-content polydimethylsiloxane layer of said polydimethylsiloxanesheet in such a way that a spacing between adjacent said metal patternsis 1,000 nm or less, and a step of releasing said polydimethylsiloxanesheet from said support substrate.
 2. A method of manufacturing anoptical element, comprising: a step of, given a low-molecular-weightsiloxane of a cyclic structure represented by [—Si(CH₃)₂O—]_(k) where kis an integer of 3 to 20 inclusive, coating a support substrate with araw material for forming a low-content polydimethylsiloxane layer thatcontains said low-molecular-weight siloxane in a smaller amount to forma coating film for the low-content polydimethylsiloxane layer, a step offeeding a raw material for forming a high-content polydimethylsiloxanelayer that contains said low-molecular-weight siloxane in a largeramount on said coating film for the low-content polydimethylsiloxanelayer and pressing a mold substrate against said raw material therebyforming a coating film for the high-content polydimethylsiloxane layerbetween said mold substrate and said coating film for the low-contentpolydimethylsiloxane layer, after which said mold substrate is releasedfrom said coating film for the high-content polydimethylsiloxane layer,a step of curing said coating film for the low-contentpolydimethylsiloxane layer and said coating film for the high-contentpolydimethylsiloxane layer into a polydimethylsiloxane sheet comprisinga structure of the low-content polydimethylsiloxane layer and thehigh-content polydimethylsiloxane layer, a step of forming a pluralityof metal patterns on a pattern-formation surface defined by saidhigh-content polydimethylsiloxane layer of said polydimethylsiloxanesheet, wherein said plurality of metal patterns each comprise asubstantially ring-form pattern having a notch in at least a partthereof, wherein a space of said notch is 1,000 nm or less, and a stepof releasing said polydimethylsiloxane sheet from said supportsubstrate.
 3. The method of claim 1, wherein a content of saidlow-molecular-weight siloxane in said low-content polydimethylsiloxanelayer is 1,000 ppm or less, and a content of said low-molecular-weightsiloxane in said high-content polydimethylsiloxane layer is 2,000 ppm ormore.
 4. The method of claim 1, wherein the optical element ismanufactured by forming said metal patterns by forming a resist patternon said pattern-formation surface of said polydimethylsiloxane sheet,then forming a metal layer on said pattern-formation surface via saidresist pattern, and finally peeling off said resist pattern therebylifting off the metal layer formed on the resist pattern.
 5. The methodof claim 1, wherein said metal patterns are formed by forming a metallayer on said pattern-formation surface of said polydimethylsiloxanesheet, then forming a resist pattern on said metal layer, then etchingsaid metal layer via said resist pattern, and finally peeling off saidresist pattern.
 6. The method of claim 1, wherein an underlay metallayer is formed all over said pattern-formation surface of saidpolydimethylsiloxane sheet, after which said metal patterns are formedon said underlay metal layer.
 7. The method of claim 1, wherein anunderlay metal layer is formed all over said pattern-formation surfaceof said polydimethylsiloxane sheet, after which said metal patterns areformed on said underlay metal layer, and a portion of said underlaymetal layer where said metal patterns are not formed, too, is removed byetching.
 8. A method of manufacturing a polydimethylsiloxane sheet,wherein: a step of, given a low-molecular-weight siloxane of a cyclicstructure represented by [—Si(CH₃)₂O—]_(k) where k is an integer of 3 to20 inclusive, coating a support substrate with a raw material forforming a low-content polydimethylsiloxane layer that contains saidlow-molecular-weight siloxane in a smaller amount to form a coating filmfor the low-content polydimethylsiloxane layer, a step of feeding a rawmaterial for forming a high-content polydimethylsiloxane layer thatcontains said low-molecular-weight siloxane in a larger amount on saidcoating film for the low-content polydimethylsiloxane layer and pressinga mold substrate against said raw material thereby forming a coatingfilm for the high-content polydimethylsiloxane layer between said moldsubstrate and said coating film for the low-content polydimethylsiloxanelayer, after which said coating film for the high-contentpolydimethylsiloxane layer is released from said mold substrate, and astep of curing said coating film for the low-contentpolydimethylsiloxane layer and said coating film for the high-contentpolydimethylsiloxane layer into a structure of the low-contentpolydimethylsiloxane layer and the high-content polydimethylsiloxanelayer, after which said structure is released from said supportsubstrate.
 9. The method of claim 8, wherein a content of saidlow-molecular-weight siloxane in said low-content polydimethylsiloxanelayer is 1,000 ppm or less, and a content of said low-molecular-weightsiloxane in said high-content polydimethylsiloxane layer is 2,000 ppm ormore.